Soak the calf brains in a bowl of cold water with 2 tablespoons
of vinegar about 30 minutes. Drain and carefully remove as much
of the membrane and veins as possible from the brains. Set aside.
In a small saucepan, combine 3 cups of cold water, the remaining
2 tablespoons of vinegar, a little salt and bay leaf. Bring to a
boil, and simmer for 10 minutes. Gently add the brains and
immediately remove the pan from the heat. Let the brains sit in
the liquid, covered, for 8 minutes, then transfer them with a
slotted spatula to a small bowl. Set aside.
Heat 2 tablespoons of butter in a large skillet over medium-high
heat. Add mushrooms, sprinkle with salt and black pepper, and
stir until nearly dry, about 8 minutes. Add the shallot and cook
for 2 minutes longer. Add cooked brains, and stir, breaking up
the brains, until mixture is almost pureed. Add 1/4 cup of
reserved Veal Stock to the mixture and simmer briefly until
thick. Remove from the heat, stir in parsley and adjust
seasoning. Cool mixture completely, then chill, covered.
Source: New York's Master Chefs, Bon Appetit Magazine